It is a 2002 duramax 120000 miles. Ok, the truck started to smoke real bad and knock loud then it died. I primed the fuel filter and checked it for water. Then I started it again. The truck ran fine for about 2 miles then it did it again. So I turned it off. I called a wrecker and towed it to a Chevy shop. Well the shop called me and told me the starter was not working so they couldnt do the injector test which takes 15 seconds of turning the engine over to get fuel results. Well my starter was working in the first place and they burned it up. Also the chey mechanic called a local starter repair shop to see if he could repair the starter. But it wasnt their fault. So I had the truck towed from the chevy shop because I didnt want them to work on my truck since they didnt take responsiblility for the starter. So I took the truck and had a new starter put in. The mechanic that put the Starter in told me that there was alot of diesel fuel on the bottom of the engine. Know I have the truck at another chevy shop and they are telling me that the return full line on the driver side head is Stripped out and I have to replace the Head. According to the service manager at the second shop the 1st shop in order to do the test would of had to remove the return line from the head and tie in there to do the test. Any Ideas on how hard it is to strip that bolt out? And how do I proceed with this problem.